Solenoid actuated unit injectors for controlling the admission of fuel to diesel engines, particularly heavy duty trucks and marine engines, have been in common use for a number of years. Early on, the fuel control valve for admitting fuel to the pressure chamber of these devices was mechanically actuated. In more recent years, the solenoid actuated control valve has become more popular and useful in light of its quick action and the fact that it can be easily and accurately programmed with current electronically controlled engines and software systems. An example of such a unit injector is shown in U.S. Pat. Nos. 4,392,612, 4,618,095, and 4,741,478 assigned to the assignee of the present invention.
The concept of substituting for the solenoid actuated unit injector, a system comprising a solenoid actuated unit pump in fluid communication with a respective injector nozzle, as a separate device, is also becoming popular. An example of such a system is shown in U.S. Pat. No. 3,779,225.
It will be noted in either case, i.e. with the solenoid actuated unit injector or the solenoid actuated unit pump, there is provided an electromagnetic coil for energizing an armature which is attached to a fuel control valve, which admits fuel to a pressure chamber (either in the pump or in the injector body depending on the device). Most commonly, the control valve with attached armature plate is spring biased to a normally open position with the electromagnetic coil being in an unenergized state. Upon energization of the electromagnetic coil, the control valve, in the form of a sliding reciprocating valve, is closed momentarily until the electromagnetic coil is next deenergized. Also most commonly, as shown in both of the above referenced patents, the chamber or cavity within which the armature resides is fuel filled to provide equalization of pressure on all sides of the reciprocating fuel control valve and to allow a certain degree of damping on the action of the armature plate as the electromagnetic coil is repeatedly energized and deenergized. This also helps control valve bounce which refers to the action of the control valve returning home on its valve seat as the valve is closed.
In both of the above-referenced systems, it is common to secure the armature plate to the control valve by means of a flathead countersunk screw in such a manner that the screw head faces the surface of the armature that is exposed to the electromagnetic coil and the screw shank is embedded within the control valve.
Prior to the present invention, this flatheaded countersunk screw has included a recessed socket head so that it can be screwed home into the control valve by means of a socket wrench having an Allenhead, or hexagonal fluted configuration.
Most recently, due to operating demands being made of the solenoid for more finite control of fuel emissions, including such things as pilot injection which requires increasing the frequency of reciprocation of the control valve, it has been noted that the socket pocket in the armature fastener is a source of cavitation erosion. This is believed to be caused by the changing state of the fuel from a fluid to a gaseous state, and resultant gas bubbles being compressed and, in effect, exploding in the recess of the cavity thereby releasing energy and causing erosion.
As a complement to the elimination of the armature plate and fastener as a source of cavitation erosion, the present invention is directed towards improving the strength of the magnetic field across the armature plate, and thus the hysteresis characteristics of the armature and fuel control valve of which it is a part.
The present invention is directed toward eliminating the armature plate and fastener as a source of cavitation erosion, and in facilitating the assembly of the armature plate to the control valve.